mustard tree has 4 distinct synonyms spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
evergreen South American shrub naturalized in United States; occasionally responsible for poisoning livestock
glabrous or pubescent evergreen shrub or tree of the genus Salvadora; twigs are fibrous and in some parts of the world are bound together in clusters and used as a toothbrush; shoots are used as camel fodder; plant ash provides salt
Synonyms, antonyms and the broader and narrower relations for mustard tree come from Princeton University’s WordNet. Full sources and licences.